This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-275085, filed Sep. 11, 2000, No. 2000-275089, filed Sep. 11, 2000; and No. 2000-275090, filed Sep. 11, 2000, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a confocal microscope using a confocal disk to obtain a sectioning image and a height measurement method using the confocal microscope.
2. Description of the Related Art
In recent years, with high integration of LSI, the number of electrodes of an LSI chip has increased, a packaging density has also increased, and a bump electrode has been used as the electrode of the LSI chip from such background.
A so-called flip chip connection is performed in which the LSI chip with such bump formed therein is laid upside down in contact with a substrate, and a bump is connected to an electrode on the substrate.
In this case, it is naturally important to accurately connect the electrode on the substrate to the bump, and it is therefore necessary to accurately form the shape and height of the bump.
As a solution, an optical height measurement apparatus in which the bump is used as a measurement object to optically measure the height of the bump has been proposed (see Jpn. Pat. Appln. KOKAI Publication Nos. 9-113253, and 9-126739). A laser scanning system or a disk system (Nipkow disk) is known as a confocal optical system of the optical height measurement apparatus, and either system has a function of converting the distribution of a height direction (light axis direction, that is, Z-axis direction) to a detected light intensity.
By this confocal optical system, a plurality of slice images are obtained for each movement position of the Z-axis direction of a sample, an IZ peak position is estimated from the maximum luminance of respective pixels of these slice images, and height information of the sample is obtained.
Additionally, when the focal point position of the Z-axis direction of the sample is moved in order to obtain the plurality of slice images, it is general to move a sample stage or an objective lens with the sample laid thereon in the Z-axis direction.
According to a sample stage movement system for moving the sample stage in the Z-axis direction, for example, when the bump height of the LSI chip formed as the sample on a large-sized 8-inches wafer is measured, the sample stage for vertically moving the 8-inch wafer with a high precision is required, and a very large-scale mechanism results. Therefore, a conventional apparatus becomes very expensive. Additionally, since the conventional apparatus also has a large mass, it is difficult to control vertical movement in a high speed, movement precision of a focal point is deteriorated, and movement also takes time. In an objective lens movement system in which the objective lens is moved in the Z-axis direction, to realize high-speed inspection in measuring the bump height of the LSI chip, the objective lens having a low magnification is used to obtain a optical system having a broad field of view, for example, having an optical system total magnification of about one time. Since this low-magnification objective lens has a large size and mass, it is difficult to control the vertical movement in the high speed. Even in this case, the movement precision of the focal point is deteriorated, and additionally the movement takes much time.
To realize the high speed of inspection, it is effective to use the low-magnification objective lens with which a large area can be observed at once and to raise a scanning speed of a two-dimensional direction. In general, a sectioning effect is valid with a larger NA of the objective lens, but the objective lens having a large NA usually has a high magnification and narrow field of view. That is, the high speed of the inspection is contradictory to the sectioning effect of a light axis direction. Therefore, in general, a high-speed inspection is performed by a low-magnification objective lens. Thereafter, when some defective portions are to be enlarged and observed, the objective lens is changed and adapted to indicate a high magnification. With the change, it is necessary to replace a rotary disk with another rotary disk in which a pinhole with a diameter corresponding to the magnification of the objective lens is formed.
However, the mechanism in which the objective lens and rotary disk are replaced in order to change the magnification has a remarkably large scale, and has a large-sized and complicated constitution. When the objective lens and rotary disk are replaced, the speed cannot be raised because of the size of the mechanism, and much changeover time is required.
On the other hand, to realize the high-speed inspection, it is proposed to use a special objective lens having large NA and low magnification, in which a broad view of field is secured at a certain degree of low magnification, and a high contrast can be realized by the sectioning effect. However, the objective lens is effective in measuring the height at a high speed, but a pixel resolution in a plane direction crossing at right angles to a light axis is not high. Therefore, in order to perform the enlargement/inspection of the defective portion, it is still necessary to replace the objective lens with the objective lens having a high magnification. Therefore, a plurality of special and expensive objective lenses having different magnifications are required, and this is economically disadvantageous.
There is also proposed a method of disposing variable magnification optical systems before and after the rotary disk, and replacing the objective lens simultaneously with varying of the magnification, so that it is unnecessary to replace the rotary disk and it is possible to prevent the sectioning effect from being deteriorated (see Jpn. Pat. Appln. KOKAI Publication No. 9-230245). Although this method is very effective, when the usual objective lens is used to perform observation with various magnifications, but it is necessary to replace the objective lens in accordance with the magnification depending on an object to be observed. Therefore, the replacement mechanism of the objective lens is large-sized, requires much time for replacement, and becomes expensive.
There is disclosed a technique of using I-Z characteristics (characteristics that a light intensity I is largest with a sample in a focal point position and the light intensity I decreases farther from the focal point position), disposing a rotary plate having a plurality of parallel plane glass plates mounted in the rear of the objective lens, and rotating this rotary plate at a high speed to move the focal point position and a relative position of the sample in Z-direction at a high speed (see Jpn. Pat. Appln. KOKAI Publication No. 9-126739). In this technique, the focal point position is discretely moved in accordance with the thickness of the parallel plane glass plate so that a slice image is obtained. In this case, the number of slice images is the same as that of parallel plane plates. A measurement range along Z direction is determined by the thickness of the thickest and thinnest parallel plane plates, and a sampling interval of the Z direction can be set to be fine with a larger number of parallel plane plates. In this manner, from the I-Z characteristics determined by a plurality of discrete slice images and the NA of the objective lens of the confocal optical system, an interpolation processing is performed in the Z direction, the focal point position of each pixel is estimated, and the speed of the height measurement of the sample can be raised.
The use of the confocal optical system is effective, when the bump becomes large to a certain degree. However, with a smaller bump, a problem occurs that much measurement time is required. That is, with an advance in miniaturization of the bump, for the CCD for use as a photodetector, it is naturally necessary to reduce a pixel size for image pick-up. Therefore, when the total magnification of the sample and CCD is the same, it is necessary to use the CCD having a much smaller pixel size. In this case, since an expensive CCD camera having a large number of pixels is used, and the image has an increased number of pixels, much time is required for a data processing. When the CCD having the same pixel size is used, the total magnification needs to be raised so as to reduce an actual field of view (range able to be imaged by the CCD). In this case, since the actual field of view is reduced, a scanning time naturally increases.
On the other hand, with the use of a device having a two-dimensional arrangement in which a train of regularly arranged pinholes is disposed in one plate, when the bump is miniaturized, a high density (a reduced pitch between the pinholes) is required for a pinhole pattern having the two-dimensional arrangement. Furthermore, since the device having the two-dimensional arrangement and the CCD camera are arranged in an optically conjugate position, it is difficult to position/adjust the respective pixels of the CCD camera and the device having the two-dimensional arrangement. Additionally, when the pitch between the pinholes is reduced, a light deviating from the focal point position (the light out of focus) enters via the adjacent pinhole, and therefore the sectioning effect drops.
An object of the present invention is to provide a confocal microscope in which a focal point can be moved at a high precision and speed, and a magnification of a sectioning image having a low magnification can easily be varied. Another object of the present invention is to provide a height measurement method using a confocal microscope with which a high-precision height measurement can be performed in a short period of time.
According to the present invention, there is provided a confocal microscope in which a sample is irradiated with an irradiation light through a confocal disk to obtain a sectioning effect, and the light from the sample is formed into an image in photoelectric conversion means through the confocal disk, the microscope comprising: an objective image formation optical system including an image formation lens to form the image of the confocal disk on the sample and an objective lens having a low magnification; and image formation lens driving means for moving the image formation lens in a light axis direction.
According to the confocal microscope of the present invention, when the image formation lens is moved, the movement precision of a focal point can rapidly be enhanced.
Since the image formation lens can be small-sized and lightweight, movement control is enabled at a high speed, and a time for moving the focal point can remarkably be shortened.
According to the present invention, there is provided another confocal microscope in which a sample is irradiated with an irradiation light through a confocal disk to obtain a sectioning effect, and the light from the sample is formed into an image in photoelectric conversion means through the confocal disk, the microscope comprising: a first image formation optical system which forms the image of the confocal disk on the sample through an objective lens having a low magnification, and which forms the light from the sample into an image on the confocal disk; and a second image formation optical system which forms a sectioning image by the first image formation optical system with respect to the photoelectric conversion means with a varied image formation magnification.
When a variable magnification optical system is set to a low magnification in a high-speed inspection and to a high magnification in enlargement/inspection of a defective portion, a high-speed broad range inspection and enlargement/inspection of the defective portion can easily be performed.
According to the present invention, there is provided a height measurement method in a confocal hap microscope in which a sample is irradiated with an irradiation light through a confocal disk to obtain a sectioning effect, and the light from the sample is formed into an image in photoelectric conversion means through the confocal disk, the microscope comprising: a first image formation optical system including an image formation lens which forms the sectioning image obtained through the confocal disk on the sample and an objective lens having a low magnification; a second image formation optical system which forms the sectioning image by the first image formation optical system on the photoelectric conversion means; and image formation lens driving means for moving the image formation lens in a light axis direction, the measurement method comprising: moving the image formation lens in a light axis direction; obtaining an IZ peak position from luminance information of pixels of a plurality of sectioning images formed by the photoelectric conversion means; and obtaining height information of the sample. According to the height measurement method of the present invention, a height in a broad range is measured at once, the speed of focal point movement can be raised, and precision and measurement range of the height measurement can be enhanced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.